Questions & Answers about Kunpa olisin luottanut vaistooni!
Why is the verb in the conditional perfect form (olisin luottanut)?
The particle kunpa (if only) triggers the conditional mood to express a wish. Because the speaker is regretting something that already happened, we use the past conditional (conditional perfect). If it were a wish about the present or future, it would just be the present conditional: Kunpa luottaisin... (If only I trusted...).
Why does the word for instinct (vaisto) take the illative case here?
In Finnish, the verb luottaa (to trust or to rely on) requires the target of the trust to be in the illative case (the "into" case). You aren't trusting "your instinct", you are trusting into it.
If the illative form of vaisto is vaistoon, why doesn't it become vaistoonni when we add the possessive suffix -ni?
When you add a possessive suffix like -ni (my) to a word in the illative case, the final -n of the illative ending drops off. So, vaisto + on (illative) + ni (my) becomes vaistooni, not vaistoonni.
Could I add the word minä (I) to this sentence?
You could say Kunpa minä olisin luottanut..., but it is unnecessary. The first-person subject is already clearly shown twice: by the -n at the end of olisin and by the -ni on vaistooni. In standard Finnish, the pronoun is usually dropped here.